Piston



V. VOSTREZ June 8, 1 943.

PISTON Filed Nov. 22. 1940 Fig. 1

Fig. 3

Fig.2

INVENTOR. victor Vb BY 6] I b sfrcz A TTORNEYI.

Patented June 8, 1943 UNITED STAES i Price 10 Claims.

lfhe present invention relates to pistons of the nature of the piston described in my prior Patent No. 2,213,775, issued September 3, 1940.

In general, the objects of the present invention are similar to those of my prior Patent No. 2,218,775, except that a number of these objects are accomplished by constructions which give better results than those of the prior construction.

In addition, an important object of the present invention is the provision of a piston head and a skirt which include intimately interfitting stub and socket members which are under tension and compression.

Another of my objects is the provision of a novel method of uniting a piston head and skirt having interiitting stub and socket portions, the method consisting in the steps of expanding the socket member under heat and then placing the stub and socket portions into their interfitting position, and in finally causing the shrinkage of the socket portion on the stub portion with the result that the socket portion will be under tension and the stub portion will be under compression.

Having in view these objects and others which will be 'pointed out in the following description, I will now refer to the drawing, in which Figure l is a median vertical sectional view of my piston, the section being in the median plane of the pin bosses.

Figure 2 is a bottom plan view of the'piston.

Figure 3 is a sectional view of a fragment of my piston showing a modified construction.

The piston includes a head It] and a skirt H which are provided with ribs l2 and I3 respectively; The head Hi and the skirt H are each integral with their ribs, being so formed in the casting operation. The head It is provided with the usual ringgrooves I4 and with the oil grooves Ma projecting inwardly. Projecting inwardly from the skirt I are two pin bosses l5 which are in alignment with each other and diametrically opposed to each other.

The present construction differs from my prior construction and, so far as I am aware, from all other prior constructions in the intimate relation between the piston head I!) and the skirt I due to thermostatic action. Arising from the top of the piston pin bosses |5 are the stub portions 213 of the standards having bores l5 for loosely receiving the reduced shanks of the screws H. The stub portions 20 seat in the socket portions 2| of the standards of the piston head If] as shown in Figure 1. The important factor is that the internal diameter of the socket portions 2| of the piston head must be lessthan the external diameter of the stub portions 25] so that the portions 2| can be made to receive the portions 20 only by enlarging the diameter of the bases of the portions 2| of the head so that the bores will receive the stub portions. This is done by heating and thus expanding the portions 2| after which the head l0 may be placed in the position shown in Figure 1 and allowed to shrink. Care must be taken, however, to so design the stub and socket, portions as to diameters that the shrinkage of the socket portion about the stub portion will not result in rupture of the socket portion.

Other departures from the construction described'in my prior patent are made either necessary or desirable by the novel manner in which the piston parts are assembled. The socket portions 2| must be heated before the piston head can be fitted on the stubportions 20 of the skirt H. The screws l'l are then drawn tight to secure the head is and the skirt together but with the screws under permanent tension; For preventing accidental 'displacementduring op'e'ra I tion,lock'ing pins 22 are employed to hol'd the' screws against all turning movement;

In pistons of the usual diameter the above described construction functions admirably but in largerpistons' it may be desired to reinforce cer- I tain parts of the piston head by encircling those;

parts with steel bandsj25, the tensile strength of which is greaterthan that of the material of which the head is formed. I

In Figure 3 I show how a similar result may 1 be obtained by casting the head It) on the skirt The projection or stub portion 2!). takes the place of the stub portion 20. The stub portion 29' is integral with the pin bosses l5 of the skirt i It is provided with annular ridges 26 or the 3 equivalent to be embedded intimately in the socket portion 2| of the head It). The projoc-,

tion 26' must be above the melting point of the material in the piston head Ill while the casting of the headis in progress so that the materials come to the closest possible proximity and when the cooling begins, the material in the head will shrink more than the contraction of the material in the skirt It and in the projection 20' thereby filling a shrink fit. This may be: accomplished in any of several ways such as by inducing a current of electricity to flow in the parts to be heated. f

It is possible with either type of joint to; place an oil ring groove in the top portion ofthe skirt 5 shown at I ia in Figure 3, and the piston ring grooves in the piston head as usual so that the life of the oil ring will be increased and carbonization will be decreased. This increase in the life of the oil ring groove follows from the fact of the lower temperatures of the upper portion of the piston skirt resulting in better lubrication and in less carbonization.

The head Ill preferably is formed of an aluminum alloy and the skirt H is formed from an iron alloy. In my construction, the head and the skirt are so intimately interconnected that the piston is substantially integral. Owing to the diiference in the coeflicients of expansion and the fact that the metals are under continuous tension and compression, no wear is possible.

The thermostatic action of the piston is of great importance. Referring to Figure 2, the character D represents the piston diameter across the pin bosses when the parts are at ordinary temperature while the piston is idle and friction is at a minimum. The character d represents the piston diameter across the working surface at ordinary temperature. With an increase of temperature t the two piston diameters may be designated by the characters D and d. The character L designates the distance between the piston head standards 20 at ordinary temperatures. The characters a and 41 represent the coeflicients of expansion of aluminum and iron alloys respectively. The thermal expansion of the skirt portion alone in the direction D for any rise in temperature t will be As the head element H) has a higher coeflicient of thermal expansion, it will increase the expansion of the skirt by an amount Lt (a-a) so that the total expansion is and since the circumference is not appreciably to be stretched, any increase in. diameter in the direction D due to the influence: of the head element on the skirt element, will result in an amount Lt (a-a) subtracted from the increase in diameter in the direction d. Therefore wear. This is entirely eliminated by the use of my piston.

Having thus described my invention in such full, clear, and exact terms that its construction and operation will be readily understood by others skilled in the art to which it pertains, what I claim as new and desire to secure by Letters Patent of the United States is:

l. A piston comprising a skirt of a relatively low expansion metal and a head of a relatively high expansion metal, means for securing said head to said skirt at points spaced inwardly of the outer surfaces of said head and said skirt, the distance between said points of connection being so related to the diameter of the piston skirt across the working surfaces thereof that the product of said distance and the difference between the coefiicients of expansion of the high expansion metal and the low expansion metal is equal to the product of the diameter across the working surface and the coefficient of expansion of the low expansion metal of the skirt, so that the diameter of the piston skirt across the working face thereof remains substantially constant.

2. A piston comprising a skirt of a relatively low expansion metal and a head of a relatively high expansion metal, pin bosses integral with said skirt and projecting inwardly therefrom, means for securing said head to said pin bosses at points spaced inwardly of the outer surface of said head and said skirt, said head being spaced from said skirt at all other points, the distance between said points of connection being sorelated to the diameter of the piston skirt across the working surfaces thereof that the product of said distance and the difference between the coefiicients of expansion of the high expansion metal and the low expansion metal is equal to the product of the diameter across the working surface and the coefiicient of expansion of the low expansion metal of the skirt so that the diameter of the piston skirt across the working face thereof remains substantially constant.

3. A piston comprising a skirt having integral 145 opposed inwardly extending pin bosses and integral tubular stub portions extending upwardly As will be obvious from the last formula, d

will equal d when Lt(a'a) =dta, or when L(a'a) :da. When this relationship is maintained, the piston diameter across the working surface remains constant. While the distance D will vary, this has such a value that it is never in excess of the diameter of the cylinder bore.

The thermostatic action of the above described piston is of prime importance as it makes possible the close interfitting of the piston in the cylinder and in the close contact with the cylinder walls under all of the fluctuations in temperature while the motor is in operation. There is no danger of the clearance between the piston and the cylinder walls becoming less as the temperature increases. The life of the motor will be greatly increased since there is no danger of scored cylinders and pistons. Prior constructions attempt to compensate for such variatlons by means of a slitted skirt but this solves the problem only partially and imperfectly. My construction contemplates the use of a skirt without a slit.

This feature increases in importance as the size of the pistons increases. In very large motors, the clearance allowance when cold must be great so that the running clearance will be sufiicient. These large cylinders result in noise or excessive therefrom, a head having an upper ring grooved portion of substantially the same exterior diameter as the skirt and a plurality of socket portions engaged over said stub portions, said socket portions being under tension by shrinkage about said stub portions.

4. A piston comprising a skirt having integral opposed inwardly extending pin bosses and integral tubular stub portions extending upwardly therefrom, a head having an upper ring grooved portion of substantially the same exterior di-' edly engaged with the upper portion of said head,-

each of said screws being under longitudinal tension due to shrinkage.

5. A piston comprising a skirt having integral opposed inwardly extending pin bosses and integral tubular stub portions extending upwardly therefrom, said skirt being of a low expansion metal, a head of high expansion metal having an upper ring grooved portion of substantially the same exteriordiameter as the skirt and a plurality of socket portions engaged over said stub portions, said socket portions being under tension by shrinkage about said stub portions, and a screw associated with each of said interfitting socket and stud portions, said screw freely extending through said stub portion with its head abutting the base thereof and with a screw threaded por tion threadedly engaged with the upper portion of said head, each of said screws being under longitudinal tension due to shrinkage.

6. A piston comprising a skirt having integral opposed inwardly extending pin bosses and integral tubular stub portions extending upwardly therefrom, said skirt being of a low expansion metal, a head of high expansion metal having an upper ring grooved portion of substantially the same exterior diameter as the skirt and a plurality of socket portions engaged over said stub portions, said socket portions being under tension by shrinkage about said stub portions, and a fastening member associated with each of said interfitting socket and stub portions, said fastening member engaging the base of said stub portion and being secured to the upper portion of said head and being free at all intermediate points thereof, each of said fastening members being under longitudinal tension due to shrinkage, and the distance between said fastening members being such that the product of said distance and the difierence between the coefiicients of expansion of the high expansion metal and of the low expansion metal is equal to the product of the diameter across the working surface and the coefficient of expansion of the low expansion metal of the skirt so that the diameter of the piston skirt across the working face thereof remains substantially constant.

7. A piston comprising a skirt having integral opposed inwardly extending pin bosses and integral stub portions extending upwardly therefrom, a head having an upper ring grooved portion of substantially the same exterior diameter as the skirt and a plurality of socket portions engaged over said stub portions, said socket portions being under tension by shrinkage about said stub portions, and a screw disposed adjacent each of said interfitting socket and stub portions and extending between said skirt and said head to retain them together, each of said screws being under longitudinal tension due to shrinkage.

8. A piston comprising a skirt having integral opposed inwardly extending pin bosses and integral tubular stub portions extending upwardly therefrom, a head having an upper ring grooved portion of substantially the same exterior diameter as the skirt and a plurality of socket portions engaged over said stub portions, said socket portions being under tension by shrinkage about said stub portions, and a screw extending through each hollow stub portion with its head abutting the base thereof and with a screw threaded portion threadedly engaged with the upper portion of said head.

9. A piston comprising a skirt having integral opposed inwardly extending pin bosses disposed intermediate the upper and lower ends of the skirt, and a head having an upper ring-grooved portion of substantially the exterior diameter of the skirt and a lower portion extending downwardly into the skirt in spaced relation thereto, and secured to said bosses to support the head directly from the bosses and in spaced relation to all other parts of the skirt, said skirt being formed with an oil ring groove so that the oil ring carried thereby is protected from the heat to which the head is subjected.

10. A piston comprising a skirt having integral opposed inwardly extending pin bosses disposed intermediate the upper and lower ends of the skirt, and a head having an upper ring-grooved portion of substantially the exterior diameter of the skirt and spaced lower projections extending downwardly into the skirt in spaced relation thereto and secured to said bosses to support the head directly from the bosses and in spaced relation to all other parts of the skirt, said skirt being formed with an oil ring groove so that the oil ring carried thereby is protected from the heat to which the head is subjected.

VICTOR VOSTREZ. 

